In J. Vac. Sci. Technol. 16 (1970) 1880 (especially FIG. 1), Sharp et al. describe an ion beam gun in the case of which a plasma is produced using a heating filament. The cations formed are held together in a field produced by permanent magnets or electromagnets, extracted from the ionization chamber using an extraction electrode and directed in the form of one or more beams (4 beams in FIG. 1) onto a substrate.
In the case of this known ion beam gun, the following features are, however, not satisfactory. Owing, especially, to the inhomogeneous magnetic field, the greatest field density of which lies approximately in the axis of the ionization chamber, the gas discharge is inhomogeneous. Because of this inhomogeneity, a complicated and expensive perforation must be made in the extraction electrode. It is not possible to achieve any desired shape of beam cross-section or any desired size of beam cross-section. Furthermore, there are restrictions with respect to the selection and durability of the material of the heating filament. Only limited use can be made of reactive ionization gases. Finally, in addition to the use of magnets, the expense of four supplies of current is not very satisfactory.
In the case of the known dual plasmatron, apart from the fact that a heating filament is not used, but the ion beam is produced using two plasmas, this known device has corresponding disadvantages (development by, inter alia, Schott).